With the development of wireless multimedia service, the demands of people for high data rate and user experience are gradually increased and thus higher requirements are raised to system capacity and coverage of the traditional cellular network. In another aspect, the popularization of applications such as social network, near-field data sharing and local advertisement enable people to understand nearby interested people or things and communicate the people, i.e., the demands for proximity services are gradually increased. The traditional cell-based cellular network has obvious limitations in the aspects of support of high data rate and proximity services. Under the background of this demand, a Device-to-Device (D2D) technology which represents a new development direction of future communication technology emerges. By adopting the D2D technology, the burden of the cellular network can be relieved, the battery power consumption of user equipments can be reduced, the data rate can be improved, the robustness of network infrastructure can be improved and the requirements of high data rate service and proximity services are well satisfied.
The D2D technology can work at authorized frequency bands or unauthorized frequency bands and allows a plurality of user equipments which support a D2D function, i.e., D2D User Equipment (UE) to directly discover or directly communicate under the situation that there is network infrastructure or there is no network infrastructure. The application scenarios of D2D mainly include three types:
1) UE1 and UE2 perform communication under coverage of a cellular network, e.g., mode 1 illustrated in FIG. 1, in which user plane data do not pass through network infrastructure;
2) UE in weakly covered areas or non-covered areas perform communication through UE relay covered by a network, e.g., mode 2 illustrated in FIG. 1, in which UE4 with poor signal quality is allowed to communicate with a network through proximity UE3 covered by the network, such that an operator can be helped to expand coverage and improve capacity;
3) Direct communicate between UEs are allowed under a situation that a cellular network cannot normally work in case of earthquakes or emergency situations, e.g., mode 3 illustrated in FIG. 1, in which a control plane and a user plane between UE5, UE6 and UE7 perform one-hop or multi-hop data communication not through network infrastructure.
The D2D technology usually includes a D2D discovery technology and a D2D communication technology:
1) The D2D discovery technology refers to a technology which is used for judging or determining that two or more D2D user equipment are proximity with one another (e.g., within a range that D2D direction communication can be performed) or is used for judging or determining that a first D2D user equipment is proximity to a second D2D user equipment.
2) The D2D communication technology refers to a technology that partial or all communication data between D2D user equipment can be directly communicated not through the network infrastructure.
In D2D communication, in one aspect, D2D UE needs to avoid missing D2D communication data which possibly need to be received, in another aspect, since the D2D UE receives D2D Scheduling Assignment (SA) by adopting a blind detection mode, if a D2D SA receiving resource pool which needs to be monitored is greater, a great amount of UE power consumption will be caused. In addition, when the D2D UE monitors the D2D SA receive receiving resource pool, cellular communication or D2D sending cannot be simultaneously performed, and thereby the cellular communication or D2D sending will be influenced since monitoring time of D2D SA is too long.